A headway distance maintenance assisting system that changes the reaction force to operation of the accelerator pedal according to the headway distance from the preceding vehicle is described in Japanese Kokai Patent Application No. Hei 10[1998]-166890. With this system, the headway distance to the preceding vehicle is detected, and the reaction force acting on the accelerator pedal is increased in conjunction with a decrease in the headway distance from the preceding vehicle in order to arouse the driver's attention. On the other hand, when there is no preceding vehicle or the preceding vehicle is far ahead, control for changing the operation reaction force is not performed. In another scheme, there are devices characterized by the fact that when the presence of a preceding vehicle is detected, the reaction force is increased in pulsed fashion, and the driver's attention is aroused when this increased reaction force is noticed. Such a scheme is described in Japanese Patent No. 3573134.